Police have arrested a man over the alleged indecent assault of a university student on a campus in Sydney's north.

Early last Thursday, the 20-year-old Macquarie University student allegedly awoke to find a man assaulting her in her bedroom.

The attack happened in the student housing accommodation in Marsfield, where it has emerged that up to 80 asylum seekers are being housed in a deal struck by the Red Cross and the company running the student accommodation.

There are also claims that campus security staff failed to inform police of the incident for several hours, which has been described by university deputy vice chancellor Deidre Anderson as a "serious issue".

Police arrested a 21-year-old Sri Lankan national at Central Station about 10:15am (AEDT) today and took him to Surry Hills for questioning.

Immigration Department spokesman Sandi Logan said on Twitter that the man was a Sri Lankan asylum seeker but that he was not a resident of the campus nor a Red Cross client.